This invention relates to the detection of receiving apparatus. More particularly this invention relates to methods and apparatus for detecting the presence and location of a receiver unit such as an enemy radar unit.
In many situations it is desirable and necessary to detect the presence of a receiver unit. For examples in electronic warfare a requirement often exists to detect the presence and location of an unfriendly radar unit or radio receiver (herein generally denoted as a target receiver). Although a target receivers or the structure in which it is housed, may present sufficient radar cross section to permit detection by ordinary radar surveillance, prior art radar systems have not been capable of adequately separating the signal reflected from the target receiver from the "clutter", i.e. signals reflected from other radar-reflective structure. Although attempts have also been made to detect the presence of an unfriendly radar unit, or other receiver-transmitter combinations (transceivers) by detecting the signals transmitted by the transceivers this technique first requires that the transmitter of the enemy transceiver be operating, and secondly requires either a priori knowledge of the enemy operating frequency or a rather complex system for monitoring a complete range of frequencies.
Accordingly, it is an object of this invention to provide a method and apparatus for detecting the presence of a target receiver unit that is free from the clutter problem which has beset the prior art.
It is another object of this invention to provide an electromagnetic surveillance system and method for detecting the presence of a target receiver unit that is effective even though the target receiver unit is not energized.